Brachytherapy is a minimally invasive method of irradiating a tumor (e.g. a prostate carcinoma, a cervical carcinoma, a breast carcinoma or a laryngeal carcinoma) using internal radiotherapy, i.e. introducing a radioactive material into the immediate vicinity of the tumor or into the tumor in order to destroy it by radioactive irradiation. To do this, what are known as “applicators” are introduced into the body near to or directly into the tumor. Such an applicator can for example comprise a puncture needle which can for example be 20 cm long and 5 mm in diameter. Using such an applicator the radioactive material, the actual radioactive radiation source, can be introduced in the form of a “seed”. The radiation sources introduced can remain in the body temporarily or for a longer time.
To be able to determine the precise position of an applicator for brachytherapy, computed tomography (CT) or magnetic resonance tomography (MRT) of the region of the body to be irradiated has until now been performed before the intervention. Using a 3D image dataset obtained in this way the precise dose distribution in the target region is calculated on an irradiation planning system. A 3D image dataset can for example indicate a property of the tissue for individual volume elements of a region of the body, such as penetrability for X-rays in the case of computed tomography. Based on the ideal dose distribution on/in the tumor the number and positions of the applicators to be introduced is then determined.
This dose planning and the acquisition of the necessary radioactive material is followed by the brachytherapy itself. To this end the patient is sedated in the sterile environment of an operating room and is put into the right position for the operation. This procedure is referred to below as positioning. The applicators are then inserted. To monitor the change in position of the applicators during the operation when they are introduced into the region of the body to be radioactively irradiated, conventional 2D fluoroscopy is performed during the operation using an X-ray unit. However, because the X-ray images to be obtained only convey a two-dimensional impression and have a relatively poor soft-tissue contrast, it is not possible to determine the precise position of the applicators in this way. Following the implantation of the applicators the patient is taken out of the sterile operating room into a computed tomography system and moved into another bed there, and the position of applicators in the region of the body is checked using computed tomography. If the applicators are not at the target position calculated using dose planning, the patient is returned to the operating room and the position of the applicators is corrected. This procedure must be repeated until the position of the applicators is correct, i.e. corresponds to the desired target position.
This repositioning may cause the applicators to be displaced, which represents a source of risk for the health of the patient, as he may suffer internal injuries. In addition, a change of location from a sterile to a non-sterile environment and back entails a large risk of infection. Time and cost are also important factors during the multiple repositioning, transportation and sterilization in whether brachytherapy can be provided cost-effectively in a hospital. Furthermore, the patient is exposed less radiation dose because of the correct position of the radiation source.
Once the position of the applicators has been successfully validated, the internal irradiation can proceed with the help of the seeds. For this the patient is taken into an irradiation room, also called the afterloading room. A check on the dose administered can generally not be measured, but it is calculated via the radiation intensity of the seed and its dwell time in the applicator. The afterloading device is likewise fed the patient's irradiation data using the dose planning system. The seed or seeds are introduced in motor-driven fashion via tubes into the applicators and remain there as long as was previously calculated in the planning. This data has until now been entered manually. The radiation source can then be moved to a different position in an applicator and remain there or else be introduced into another applicator.
In brachytherapy a very precise way of working and precise position determination play a crucial role. Otherwise the soft tissue surrounding the tumor may be damaged by the radioactive irradiation. On the other hand, it is not possible to check the position of the applicators frequently during the implantation. The risk of infection during repositioning for the recordings in the computed tomography system and the increasing X-ray dose with every examination in the operating room by an X-ray unit are undesirable.